Add Steam Deck (nix-deck) configuration with Jovian-NixOS and remote building

- Add Jovian-NixOS integration for Steam Deck hardware support
- Create nix-deck machine configuration with SteamOS role
- Add jovian-compat.nix for NixOS 25.05 compatibility (remove in 25.11+)
- Create remote-build role for distributed builds
- Configure zix790prors as build host
- Configure nix-book and nix-deck to use remote builder with fallback
- Add comprehensive setup documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

machines/nix-book/configuration.nix

@@ -21,6 +21,11 @@
     };
     nfs-mounts.enable = true;
     printing.enable = true;
+    remote-build.builders = [{
+      hostName = "zix790prors";
+      maxJobs = 16;
+      speedFactor = 3;
+    }];
     spotifyd.enable = true;
     users = {
       enable = true;